earth science

Magnesiohastingsite

Magnesiohastingsite is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Magnesiohastingsite rather than just read about it. In short: Magnesiohastingsite is a calcium-containing amphibole and a member of the hornblende group. It is an inosilicate (chain silicate) with the formula NaCa2(Mg4Fe3+)(Si6Al2)O22(OH)2 and molar mass 864.69 g.

Key takeaways

Magnesiohastingsite belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Magnesiohastingsite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Magnesiohastingsite from memory before moving on to harder problems.

Reference excerpt

Magnesiohastingsite is a calcium-containing amphibole and a member of the hornblende group. It is an inosilicate (chain silicate) with the formula NaCa2(Mg4Fe3+)(Si6Al2)O22(OH)2 and molar mass 864.69 g. In synthetic magnesiohastingsite it appears that iron occurs both as ferrous iron Fe2+ and as ferric iron Fe3+, but the ideal formula features only ferric iron. It was named in 1928 by Marland P. Billings. The name is for its relationship to hastingsite and its magnesium content. Hastingsite was named for the locality in Dungannon Township, Hastings County, Ontario, Canada. Calcic (containing calcium) amphiboles include:

The tremolite – actinolite – ferro-actinolite series The hornblende group The kaersutite – ferro-kaersutite series Joesmithite The hornblende group includes:

The edenite – ferro-edenite series The tschermakite – ferrotschermakite series The pargasite – ferro-pargasite series The magnesiohastingsite – hastingsite series The magnesiosadanagaite – sadanagaite series

Unit cell Magnesiohastingsite belongs to the monoclinic crystal system, point group 2/m, space group C2/m. It has two formula units per unit cell (Z = 2). The unit cell parameters both for natural and for synthetic material are a = 9.9 Å, b = 18.0 Å, c = 5.3 Å, β = 105°.

Structure

The structure of all amphiboles is based on a double chain of linked SiO4 tetrahedra, with composition (Si4O11)n. The inner tetrahedra are referred to as T1 and the outer ones as T2. The pattern in the double chain repeats after a block of two T1 and two T2 tetrahedra, with a repeat distance of approximately 5.3 Å, and this determines the length of the unit cell along the c crystal axis. The tetrahedra within a chain all point outwards in the same direction, and the chains are linked back-to-back by cations to form I-beams. The I-beams themselves are then linked together to form the complete structure.

Optical properties The mineral is subopaque and vitreous, green to dark green or black in color and with a pale grey-green to pale brownish-green streak. It is biaxial (-) with refractive indices for natural material in the range nα = 1.652 to 1.676, nβ = 1.661 to 1.695, nγ = 1.666 to 1.706. Synthetic material has nα = 1.642 to 1.657, nγ = 1.653 to 1.672. An increase in magnesium content causes a decrease in refractive indices. The maximum birefringence (the difference in refractive index between light travelling through the crystal with different polarizations) is δ = 0.012 to 0.033. The optic angle 2V is the angle between the two optic axes in a biaxial crystal. Measured values of 2V for this mineral vary widely from about 60° to 90°. It is also possible to calculate a theoretical value of 2V from the measured values of the refractive indices. The calculated value varies from 68° to 88°. The direction perpendicular to the plane containing the two optic axes is called the optical direction Y. In magnesiohastingsite Y is parallel to the b crystal axis. The optical direction Z lies in the plane containing the two optic axes and bisects the angle between them. In magnesiohastingsite the angle between Z and the c crystal axis is 15° to 19°. If the color of the incident light is changed, then the refractive indices are modified, and the value of 2V changes. This is known as dispersion of the optic axes. For magnesiohastingsite the effect is weak, with 2V larger for red light than for violet light (r>v). Pleochroism is variable in green, yellow-green, bluish-green and brown.

Physical properties Cleavage is good with cleavage surfaces intersecting at about 56° and 124°, as is common with all the amphiboles. The mineral displays simple or multiple twinning parallel to a prism face. It is a brittle mineral, with Mohs hardness 5 to 6 and specific gravity 3.2, with increasing magnesium content causing a decrease in specific gravity. It is not radioactive and it is insoluble in hydrochloric acid.

Occurrence and associations The type locality is in the Canadian National Railway tunnel, Montreal, Quebec, Canada. It is common in amphibolite, schist and pegmatitic gabbro. It is also found in welded tuffs, granodiorite, granite and tonalite. Associated minerals include quartz, orthoclase, plagioclase, biotite, magnetite and apatite. Barkevikite and the magnesium-rich members of the hastingsite group are found in diorite, essexite and related calcium-rich rocks. Localities include:

The granitic batholiths of the Scottish Highlands The Swiss and Italian Alps The Harz Mountains, Germany Finland and Sweden Japan, where it is widespread The Southern California and Sierra Nevada batholiths, California, US Langban, Sweden, in skarn In a xenolith in diorite porphyry in the Mount Hilliers complex, Henry Mountains, Garfield County, Utah

References

External links Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=11242

Illustrations

Worked examples

Example 1 — a first encounter with Magnesiohastingsite

Start with the simplest possible case. Write down what Magnesiohastingsite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Magnesiohastingsite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Magnesiohastingsite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Magnesiohastingsite

In research: Magnesiohastingsite appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Magnesiohastingsite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Magnesiohastingsite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amphibole group, Calcium minerals, Hydroxide minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Magnesiohastingsite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Magnesiohastingsite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Magnesiohastingsite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Magnesiohastingsite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Magnesiohastingsite in simple terms?

Why does Magnesiohastingsite matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Magnesiohastingsite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Magnesiohastingsite.